Spatial pattern and process at the plant neighbourhood scale: insights from communities dominated by the clonal grass Elymus repens (L.) Gould

Question: How do clonal traits of a locally dominant grass (Elymus repens (L.) Gould.) respond to soil heterogeneity and shape spatial patterns of its tillers? How do tiller spatial patterns constrain seedling recruitment within the community? Locations: Artificial banks of the River Rhône, France. Material and Methods: We examined 45 vegetation patches dominated by Elymus repens. During a first phase we tested relationships between soil variables and three clonal traits (spacer length, number of clumping tillers and branching rate), and between the same clonal traits and spatial patterns (i.e. density and degree of spatial aggregation) of tillers at a very fine scale. During a second phase, we performed a sowing experiment to investigate effects of density and spatial patterns of E. repens on recruitment of eight species selected from the regional species pool. Results: Clonal traits had clear effects – especially spacer length – on densification and aggregation of E. repens tillers and, at the same time, a clear response of these same clonal traits as soil granulometry changed. The density and degree of aggregation of E. repens tillers was positively correlated to total seedling cover and diversity at the finest spatial scales. Conclusions: Spatial patterning of a dominant perennial grass responds to soil heterogeneity through modifications of its clonal morphology as a trade‐off between phalanx and guerrilla forms. In turn, spatial patterns have strong effects on abundance and diversity of seedlings. Spatial patterns of tillers most probably led to formation of endogenous gaps in which the recruitment of new plant individuals was enhanced. Interestingly, we also observed more idiosyncratic effects of tiller spatial patterns on seedling cover and diversity when focusing on different growth forms of the sown species.     

Increased spatial dominance in high nitrogen, saturated soil due to clonal architecture plasticity of the invasive wetland plant, Phalaris arundinacea

Clonality as a plant growth strategy has been a successful adaptation contributing to clonal plants being the dominant vegetation in many ecosystems and has been implicated as a significant factor contributing to invasiveness. The objective of this study was to determine if Phalaris arundinacea, an invasive wetland plant, modifies its clonal growth behavior when grown in high resource conditions. When grown in ideal conditions (high soil-N and moisture), we hypothesized that along with an increase in tiller production and robustness (biomass per tiller), P. arundinacea would increase the spatial spread of tiller placement (distance from parent and daughters). To test this we conducted a greenhouse study in which we grew P. arundinacea seedlings under two soil-N levels (no nitrate addition or 40 g N m^?2 year^?1) at two soil moisture levels (dry or saturated) for 10 weeks and recorded the placement (angle and distance from the parent plant) of each tiller produced. Total aboveground and belowground biomass, shoot/root ratio, and biomass per tiller were measured at the conclusion of the experiment. Plants grown in saturated conditions produced significantly more tillers that were more widely dispersed. Surprisingly, soil-N did not significantly affect most characteristics of spatial pattern, though soil-N did affect biomass production, shoot/root ratio, and biomass per tiller. These results indicate soil moisture and soil-N affect different aspects of the clonal growth behavior of P. arundinacea in the early stage of colonization. This new information provides a mechanism to explain how P. arundinacea aggressively competes for space in wetland habitats.     

Above- and Belowground Prairie Cordgrass Response to Applied Nitrogen on Marginal Land

Prairie cordgrass (Spartina pectinata, Link.) has been evaluated for its biomass potential because of its high yield, relatively low nutrient demand, and diverse geographical adaptation. Our objectives were to determine (1) biomass production potential of prairie cordgrass in South Dakota and Kansas under varying nitrogen levels, (2) the effect of N on prairie cordgrass yield components (tillers m^?2 and tiller mass), and (3) the effect of N on yield and N concentration of belowground biomass. Older stands of Red River prairie cordgrass (RR-PCG) in South Dakota and Atkins prairie cordgrass (AT-PCG) in Kansas were fertilized with 0, 56, 112 and 168 kg N ha^?1 from 2008 to 2011 in South Dakota and in 2009 and 2010 in Kansas. Experimental design at all locations was a 4?×?4 Latin square. Prairie cordgrass was harvested around a killing frost in October and early November. Biomass production ranged from 5.50 to 13.69 Mg ha^?1 in South Dakota and 5.33 to 12.51 Mg ha^?1 in Kansas. Prairie cordgrass yield did not increase significantly with N application at any location or year. Across years, tiller density ranged from 536 to 934 tillers m^?2 for RR-PCG in South Dakota and from 234 to 315 tillers m^?2 for AT-PCG in Kansas. Neither tiller density or tiller mass was affected by N rate at any location in any year. Belowground biomass production to a depth of 25 cm was equal to or greater than aboveground biomass. However, it was not affected by N rate in all locations by any year. Understanding prairie cordgrass nitrogen-use dynamics to improve biomass and nutrient management will be essential for future investigations. Findings of this study are important to support the notion that prairie cordgrass biomass production in two different environments can be achieved with minimal N inputs.     

Capturing cross-scalar variation of habitat selection with grid sampling: an example with hazel grouse (Tetrastes bonasia L.)

The objective of this study was to investigate a grid-based sampling design to determine the cross-scalar selection of habitat by a territorial animal species: the hazel grouse (Tetrastes bonasia L.). In each of three sites with increasing hazel grouse nest site density, three lattice grids were used to measure both the habitat variables and the species occurrence in 100 30?×?30 m cells. We calculated the average values for habitat variables, as well as use versus non-use by the species, at three spatial scales: small (1?×?1 cell), intermediate (2?×?2 cells) and large (3?×?3 cells). Generalised linear mixed models were integrated into a method of variation and hierarchical partitioning and used to assess the relationship between the habitat variables and the species preferences at each scale. In all scales, species selection was associated with ground layer composition. Selection was also associated with the composition of the woody layer and negatively associated with dominance of tor grass (Brachypodium rupestre (Host) Roem. & Schult.) at the two larger scales. Both litter cover and thinning contributed positively to the habitat selection at the two smaller scales. The other variables were significant only at one scale or explained a relatively low proportion of the variation at multiple scales. Neither the management nor the stand structure variables played a significant independent role across scales when compared with ground layer variables. The total variation explained was highest (ca. 90 %) at the large scale. This finding indicates the possibility of obtaining cross-scalar hazel grouse preferences from grid-based sampling, provided that spatial autocorrelation in the data is handled appropriately.     

Three approaches for analysing the dynamics ofthe horizontal layout of tillers in grass patches. Application totall fescue swards surveyed over two growing seasons

The layout of the tillers was surveyed throughout two consecutive growing seasons in almost pure tall fescue swards. These swards were periodically cut and differed in age (2 or 6 years at the beginning of the survey) and nitrogen application level (150 or 350 kg N·ha^–1·yr^–1). Ten permanent quadrats in each of the four sward types were observed four times a year, after each cut. At each observation time, each quadrat was divided into a 10 × 15 grid of 2 × 2 cm cells and the living tillers counted in each. Three approaches for analysing this survey were compared. The means of the successive tiller numbers in each cell and their variability displayed a steady background of stand structure with stable sparse and stable dense areas. The young N-rich swards have similar proportions to these zones, while the old N-poor swards have larger stable sparse areas compared to stable dense areas. Calculating the differences between two successive observations cannot easily be used to locate the disappearance and the appearance of tillers, as they can change position. Nevertheless, between consecutive observations, the young N-rich swards seemed to be less conservative than the others. The principal component analysis gives a global analysis of the dynamics. In all sward types, the steady background accounted for about 50 % of variation with the main changes being between years, which accounted for about 20 % of variation. The results bring into question the relative importance of local fertility and the processes of clonal growth in the dynamics of a grass patch.     

Patterns in the Distribution of American Beachgrass (<Emphasis Type="Italic">Ammophila breviligulata</Emphasis>) and the Density and Reproduction of Annual Plants on a Coastal Beach

Beach communities of eastern North America are commonly dominated by the native perennial grass Ammophila breviligulata. It typically co-occurs with a variety of annual grasses and herbs in the pioneer zone. To determine the potential significance of this vigorous clonal species to the annual community, density, spatial distribution, seed production and potential seed rain were quantified for three focus species (Triplasis purpurea, Cenchrus tribuloides, and Heterotheca subaxillaris) in a 45×40 m section of coastal beach on Staten Island, New York, USA. During autumn 2000, five 40 m transects (10 m apart) were established perpendicular to shore; ramet density for Ammophila, and densities and per capita seed production for the three species, were estimated in 150 contiguous quadrats (35 cm × 30 cm) per transect. Both Triplasis and Cenchrus were more likely to occur in quadrats without Ammophila. Per capita seed production of Cenchrus and Heterotheca showed a curvilinear decrease with increasing numbers of Ammophila ramets. Mean seed rain per m² was significantly reduced in the presence of Ammophila for all three focus annuals. In this beach community, Ammophila acts as an ecosystem engineer, but has a mostly negative influence on the distribution, density, and reproduction of the co-occurring annuals. Results suggest that continual, deliberate planting of A. breviligulata could be detrimental to the abundance and diversity of native annual herbs on the eastern coasts of North America.     

Infestation Rates and Tiller Morphology Effects by the Switchgrass Moth on Six Cultivars of Switchgrass

Switchgrass (Panicum virgatum L.) is a potential biomass crop for native species-based biofuel systems in North America. A recently identified pest of switchgrass, the switchgrass moth, Blastobasis repartella (Dietz) (Lepidoptera: Coleophoridae), feeds in the basal above-ground internodes and below-ground in the proaxis and rhizomes, causing premature tiller and rhizome loss. Our goal was to determine genetic and temporal variation among six upland cultivars for frequency of tiller infestation by larvae of the switchgrass moth in mature stands in the northern Great Plains and if variation in biomass production was associated with variation in frequency of infestation. Data were collected in 2011 and 2012 for tiller density, biomass, frequency of infestation, number of leaves per healthy and infested tiller, and weights of healthy and infested tillers. Differences were found among cultivars for tiller density, biomass yield, and numbers of leaves per healthy and infested tillers. ‘Summer’, ‘Sunburst’, ‘Pathfinder’, and ‘Cave-In-Rock’ were the highest yielding cultivars. Mean frequency of infestation was different between 2011 (6.7 %) and 2012 (9.6 %). Infested tillers had one less collared leaf than healthy tillers. The weights of healthy tillers were ca. 3× those of infested tillers in both years, suggesting an impact on biomass accumulation and economic value. Levels of infestation were similar for all six cultivars, indicating no feeding preference by the switchgrass moth larva among genetically diverse cultivars of switchgrass. Regression of biomass yield on frequency of infestation showed negative linear relationships for ‘Carthage’ and ‘Kentucky 1625’.     

Degradation of Abies veitchii wave-regeneration on Mt. Misen in Ohmine Mountains: effects of sika deer population

How has the degradation of Abies veitchii wave-regeneration occurred under the sika deer (Cervus nippon) pressure? We conducted tree census and ground vegetation survey in a 1 ha plot in Mt. Misen (Nara prefecture, Japan). We found 15 tree species (over 50 cm in height). Abies accounted for 60.0 % of all living trees, and 46.9 % of Abies were damaged (herbivory, bark stripping and/or fraying) by deer. Spatial distribution of Abies trees showed Abies-wave, although there were few saplings in the dieback zone. Estimated deer population density in 2009 was 57.3 head/km². Number of living Abies and standing dead conifer trees, and ground vegetation cover for each quadrat (5 × 5 m) were used to assign the quadrats into 6 clusters. The hierarchical clustering-approach revealed that living Abies distributed mainly on the moss and/or Carex fernaldiana dominated quadrats, but did not on the Dennstaedtia scabra, or Brachypodium sylvaticum dominated quadrats. While standing dead conifer trees distributed mainly on the Carex dominated quadrats, they hardly occur on the moss, the Dennstaedtia or the Brachypodium dominated quadrats. Regeneration of Abies tree and thus the wave-regeneration is hindered for now owing to deer herbivory and bark-stripping. The ground vegetation under the dieback zone has changed from the moss and/or the Carex dominated one to the Carex, the Dennstaedtia or the Brachypodium covered vegetation with the canopy remained open and without Abies regeneration.     

A measure for spatial heterogeneity of a grassland vegetation based on the beta‐binomial distribution

Abstract. A method is proposed to estimate the frequency and the spatial heterogeneity of occurrence of individual plant species composing the community of a grassland or a plant community with a short height. The measure is based on the beta‐binomial distribution. The weighted average heterogeneity of all the species composing a community provides a measure of community‐level heterogeneity determining the spatial intricateness of community composition of existing species. As an example to illustrate the method, a sown grassland with grazing cows was analysed, on 102 quadrats of 50 cm × 50 cm, each of which divided into four small quadrats of 25 cm × 25 cm. The frequency of occurrence for all the species was recorded in each small quadrat. Good fits to the beta‐binomial series for most species of the community were obtained. These results indicate that (1) each species is distributed heterogeneously with respective spatial patterns, (2) the degree of heterogeneity is different from species to species, and (3) the beta‐binomial distribution can be applied for grassland communities. In most of the observed species spatial heterogeneity is often characterized by species‐specific propagating traits: seed‐propagating plant species exhibited a low heterogeneity/random pattern while clonal species exhibited a high heterogeneity/aggregated pattern. This measure can be applied to field surveys and to the estimation of community parameters for grassland diagnosis.     

Chemical composition and ethanol production potential of Thai seaweed species

This study evaluated the potential use of several Thai seaweed species for ethanol production. The high biomass of the green algae Ulva intestinalis and Rhizoclonium riparium and the red algae Gracilaria salicornia and Gracilaria tenuistipitata in an earthen pond culture led us to select these species for our study. The seaweed species were analyzed for chemical composition, resulting in ash contents of 37.62?±?0.15 % and fiber of 11.93?±?0.16 %, with the highest values in R. riparium. Low lipid values were found in all species, with the highest value (p?<?0.05) in G. salicornia (1.69?±?0.07 %) and the lowest in R. riparium (0.28?±?0.01 %) and G. tenuistipitata (0.26?±?0.01 %). The highest carbohydrate contents were found in G. tenuistipitata (54.89 %), and the lowest were in R. riparium (29.53 %). G. tenuistipitata (8.58?±?0.36 %) and U. intestinalis (8.24?±?0.28 %) had higher sulfate contents compared with G. salicornia (4.69?±?0.04 %) and R. riparium (1.97?±?0.20 %). The monosugar algal tissue components were analyzed by HPLC; rhamnose, xylose, fucose, arabinose, mannose, glucose, and galactose were used as reference sugars. Total sugar was found to be highest in G. tenuistipitata (98.21 %). Arabinose, glucose, and galactose were the main sugar components in all species. Glucose obtained from G. tenuistipitata (6.55 %) and R. riparium (6.52 %) was higher than in G. salicornia (0.27 %) and U. intestinalis (2.78 %). G. tenuistipitata fermentation gave a higher yield of ethanol (4.17?×?10^?3 g ethanol g^?1 sugars; 139.12 μg ethanol g^?1 glucose) than R. riparium (0.086?×?10^?3 g ethanol g^?1 sugars; 33.84 μg ethanol g^?1 glucose), U. intestinalis (0.074?×?10^?3 g ethanol g^?1 sugars; 9.98 μg ethanol g^?1 glucose), and G. salicornia (0.031?×?10^?3 g ethanol g^?1 sugars; 1.43 μg ethanol g^?1 glucose).     

Above- and belowground dynamics of plant community succession following abandonment of farmland on the Loess Plateau, China

Aboveground and belowground changes during vegetation restoration and vegetation successions need to be characterized in relation to their individual responses to changes in soil resources. We examined above- and belowground vegetation characteristics, soil moisture, and nutrient status at the end of the growing season in 2006 in plots with vegetation succession ages of 2, 4, 6, and 8 years (two replicates each) that had been established on abandoned cropland, where potatoes had been grown for 3 years, using hoe and plow cultivation, immediately prior to vegetation clearance and subsequent natural plant colonization. A plant community comprising pioneer species [e.g., Artemisia capillaries, (subshrub)] was characterized by low levels of species richness (7.5?±?1.4 species m^?2), plant density (35.7?±?4.2 stems m^?2), fine root length density (940.1?±?90.1 m m^?2), and root area density (2.3?±?0.3 m² m^?2) that increased rapidly with time. Aboveground and belowground characteristics of both A. capillaries and the later successional species, Stipa bungeana (C3 perennial grass), increased in the first 6 years, but in the following 2 years A. capillaries declined while S. bungeana thrived. Thus, the fine root length density of A. capillaries, 812.4 m m^?2 after 2 years, changed by a factor of 1.7, 2.0, and 0.4 in the 4th, 6th, and 8th years, whereas that of S. bungeana changed from 278.4 m m^?2, after 4 years, and by 1.7 and 23.3 times in the 6th and 8th years, respectively. Secondary vegetation succession resulted in reduced soil moisture contents. Soil available P and N mainly influenced aboveground characteristics, while soil moisture mainly influenced belowground characteristics. However, soil moisture had no significant affect on S. bungeana belowground characteristics at the population level in this semiarid region.     

Effect of Mg, Si, and Sr on growth and antioxidant activity of the marine microalga Tetraselmis suecica

Efforts to increase the productivity of microalgal cultures have been focused on the improvement of photobioreactors, but little attention has been paid to the nutritional requirements of microalgae in order to improve culture media formulation. In this study, the main goal was obtaining a high productivity for Tetraselmis suecica (Chlorophyta) in semicontinuous culture by adding magnesium (Mg), silicon (Si), and strontium (Sr) at concentrations from 0.01 to 10 mM; at the time, the effect on steady-state cell density, biochemical composition, and antioxidant activity of T. suecica was evaluated. Because productivity is higher in high-density cultures, the work was focused many times to cell density. Mg (3 mM) and Sr (0.1 mM) added separately reached the highest steady-state cell density (7.0?×?10⁶?±?0.4 cells mL^?1) in comparison to control (4.2?±?0.1 cells mL^?1), but simultaneous addition had a synergic effect, achieving 8.7?×?10⁶?±?0.6 cells mL^?1. Silicon (3 mM) significantly affected the steady-state cell density, reaching 6.0?±?0.3 cells mL^?1 and increased the cell ash-free dry weight, reaching 127?±?7.9 pg cell^?1 in comparison to control (102.7?±?5.0 pg cell^?1), resulting in an ash-free dry weight productivity of 0.75?±?0.07 g?L^?1 day^?1. The highest fatty acids content and antioxidant activity, measured by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) method were obtained with Sr 10 mM. Sr treatments showed a high correlation (R ²?=?0.98) between DPPH inhibition and polyphenolic content, explaining its high antioxidant activity. Therefore, the addition of Mg, Si, and Sr to culture medium of T. suecica is recommended to achieve high steady-state cell density in semicontinuous cultures.     

Long-term outdoor growth and lipid productivity of Tetraselmis suecica, Dunaliella tertiolecta and Chlorella sp (Chlorophyta) in bag photobioreactors

There has been considerable interest on cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. The ideal microalga characteristics are that it must grow well even under high cell density and under varying outdoor environmental conditions and be able to have a high biomass productivity and contain a high oil content (~25–30 %). The main advantage of Chlorophyta is that their fatty acid profile is suitable for biodiesel conversion. Tetraselmis suecica CS-187 and Chlorella sp. were grown semi-continuously in bag photobioreactors (120 L, W?×?L?=?40?×?380 cm) over a period of 11 months in Melbourne, Victoria, Australia. Monthly biomass productivity of T. suecica CS-187 and Chlorella sp. was strongly correlated to available solar irradiance. The total dry weight productivity of T. suecica and Chlorella sp. was 110 and 140 mg L^?1 d^?1, respectively, with minimum 25 % lipid content for both strains. Both strains were able to tolerate a wide range of shear produced by mixing. Operating cultures at lower cell density resulted in increasing specific growth rates of T. suecica and Chlorella sp. but did not affect their overall biomass productivity. On the other hand, self shading sets the upper limit of operational maximum cell density. Several attempts in cultivating Dunaliella tertiolecta CS-175 under the same climatic conditions were unsuccessful.     

Density and Distribution of Xylocopa Nests (Hymenoptera: Apidae) in Caatinga Areas in the Surroundings of Passion Fruit Crops

Due to their importance as pollinators of many plant species, this study aimed to know the nest density, spatial distribution, and nesting substrates used by Xylocopa species in the Caatinga, a xerophilous vegetation of Northeastern Brazil. Three areas of Caatinga in the surroundings of passion fruit crops were sampled. The bee species found in these areas were Xylocopa grisescens Lepeletier and Xylocopa frontalis (Olivier). All nests were in Commiphora leptophloeos (Burseraceae) trees (n?=?113). Phytosociological analysis showed that this tree species presented the highest absolute density (212.5 individuals/ha) and index of importance value (52.7). The distribution pattern of the C. leptophloeos was aggregated. The nests were located in dead and dried branches with an average diameter of 5.3?±?2.0 cm (n?=?43). The mean number of nests/tree was 3.1?±?2.8 (n?=?113). The less disturbed area showed 6.7 nests/ha and 4.2 nests/tree. In the disturbed areas, 0.9 nests/ha and 2.4 to 2.7 nests/tree were observed. The availability of substrate for nesting in the studied areas and its importance as a limiting factor for nesting are discussed.     

Tiller demography in seashore populations of Agrostis stolonifera,Festuca rubra and Poa irrigata

Abstract. The dynamics of tillers in natural populations of three cohabiting perennial grass species, Agrostis stolonifera, Festuca rubra and Poa irrigata (= Poa pratensis ssp. irrigata) were studied for five years in a Baltic seashore meadow. The process of tiller population maintenance was very dynamic. Both birth and death rates of tillers were high, particularly in A stolonifera, and the turnover rate of the populations was high. Recruitment was mainly by vegetative tillers, produced continuously throughout the growing season. The proportion of flowering tillers was low, but varied between years. Considerable year-to-year variation was also found in birth and death rates. Despite this between-year variation and the differences found between species in flowering frequency, pattern of survivorship and tiller longevity, population sizes of the species remained relatively constant.     

Early Clonal Survival and Growth of Poplars Grown on North Carolina Piedmont and Mountain Marginal Lands

The western half of North Carolina has abundant marginal pasturelands that vary greatly in altitude. Studies have demonstrated high Populus productivity on coastal plains and eastern Piedmont regions. Our objective was to identify best-performing Populus clones on marginal pasturelands representing upper Piedmont (Salisbury, 215 m above sea level, m.a.s.l.), northern Blue Ridge Mountains (Laurel Springs, 975 m.a.s.l.), and southern Blue Ridge Mountains (Mills River, 630 m.a.s.l.). At Salisbury, height and basal diameter (BD) were significantly related to clones (p?<?0.0001), and some clones were affected by clone-spacing interaction while spacing affected aboveground wood volume significantly (p?<?0.0001). At Mills River, clonal survival (p?<?0.0011), height, and volume (p?<?0.0051) varied with contrasting significance of some clonal differences between spacings. At Laurel Springs, survival varied among clones in 1 m?×?1 m spacing (p?=?0.003) but not 2 m?×?2 m spacing while heights and volumes differed in both spacings (p?<?0.0058). Clone 185 was consistently in the top 10 % for height, BD, and survival at all sites and spacings while other clones performed variably. Height-BD regressions were affected by clones, spacing, and sites. Volume had no clear correlations with precipitation, photosynthetically active radiation, temperature, and altitude across sites while height correlated with precipitation. Our results compared favorably with published results in other US regions, and show short rotation poplars have efficacy in Piedmont and mountain regions if the right clones in terms of growth/productivity, survival, and disease resistance are selected. Larger clonal performance variations are expected as competition increases, and highlight importance of experimentally determining suitable clones for specific sites.     

Changes in soil organic carbon and total nitrogen stocks after conversion of meadow to cropland in Northeast China

Aims

Grassland conversion to cropland (GCC) may result in loss of a large amount of soil organic carbon (SOC). However, the assessment of such loss of SOC still involves large uncertainty due to shallow sampling depth, soil bulk density estimation and spatial heterogeneity. Our objectives were to quantify changes in SOC, soil total nitrogen (STN) and C:N ratio in 0–100 cm soil profile after GCC and to clarify factors influencing the SOC change.

Methods

A nest-paired sampling design was used in six sites along a temperature gradient in Northeast China.

Results

SOC change after GCC ranged from ?17 to 0 Mg ha^?1 in 0–30 cm soil layer, recommended by IPCC, across the six sites, but ranged from ?30 to 7 Mg ha^?1 when considering 0–100 cm. We found a linear relationship between SOC change in 30–100 cm and that in 0–30 cm profile (ΔC_30?100?=?0.35ΔC_0?30, P?<?0.001), suggesting that SOC change in 0–100 cm was averagely 35 % higher than that in 0–30 cm. The change in STN showed a similar pattern to SOC, and soil C:N ratio did not change at most of sites. On the other hand, SOC loss after GCC was greater in soils with higher initial SOC content or in croplands without applying chemical fertilizers. Furthermore, SOC loss after GCC decreased with falling mean annual temperature (MAT), and even vanished in the coldest sites.

Conclusions

The magnitude of SOC loss following GCC in Northeast China is lower than the global average value, partly due to low MAT here. However, the current low SOC loss can be intensified by remarkable climate warming in this region.     

Species Trials of Short Rotation Woody Crops on Two Wastewater Application Sites in North Carolina,USA

Forty-two Populus spp. clones, Eucalyptus benthamii, and seven tree species native to North Carolina were evaluated for survival and height growth through the establishment phase at two municipal wastewater application sites. Groundwater was monitored at each site to determine if establishment of the species trials resulted in exceedances of nutrient mitigation requirements. At the Gibson Wastewater Treatment Facility, 26 Populus clones had 100 % survival, with mean height growths ranging between 152 to 260 cm, and basal diameters ranging between 11.4 and 28.8 mm. Green ash, planted in 2011 and 2012, had high survivorship (>95 %) with first year mean height growth of 30?±?28 cm (2012) and second year mean height growth of 101?±?52 cm (2011). Basal diameter for green ash was 33.3?±?12.6 mm. E. benthamii had moderate survivorship (>77 %) and first year mean height growth of 47?±?27 cm. At the Jacksonville Wastewater Treatment Facility, green ash and bald cypress had high survivorship (>96 %), first year mean height growths of 14?±?25 cm and 27?±?16 cm, and basal diameters of 13.1?±?3.9 mm and 11.6?±?4.8 mm, respectively. Survivorship for 12 Populus clones ranged from 50 and 94 % with mean first year height growths between 58 to 121 cm, and basal diameters between 6.8 and 12.5 mm. E. benthamii had low survivorship (43 %) with mean first year height growths of 17?±?17 cm and basal diameters of 12.0?±?7.7 mm. Groundwater concentrations of NO₃?+?NO₂ and N-NH₄ remained below regulatory requirements at both sites with one exceedance in February 2012 in Jacksonville, NC. The results show that some Populus clones are excellent candidates for woody biomass production on municipal wastewater application fields. Native green ash and bald cypress are also good candidates, but these trees may require longer rotations than Populus to achieve similar biomass yields.     

Unexpected larval habit of Listronotus bonariensis (Coleoptera: Curculionidae) raises questions about population dynamics analysis and management

Listronotus bonariensis (Kuschel) is a pest of agriculturally important graminaceous species, with mining larvae that kill the stems of the host plants. In this study, larval populations were measured in spring and summer in irrigated dairy grassland comprising Lolium perenne L. (cv. Nui) with and without the endophyte Epichloë festucae var. lolii Latch, M.J. Chr. and Samuels and Poa annua L.. Larvae were extracted from tillers taken from the swards of these two grass species and extracted from turves, and L. bonariensis population densities were estimated from tiller and turf larval counts on a m⁻² basis. Over the study period, the total number of larvae and larval densities extracted from turves was on average 2× greater than indicated from tillers. In most seasons, larval densities from turves were significantly higher than those from the tillers, though there was no correlation between tiller and turf larval densities. Mean head capsule widths of larvae emerging from turf samples showed significant seasonal effects compared with tillers, while mean head capsule widths of all four instars were significantly greater when extracted from tillers compared with turves. There was a significant endophyte effect on head capsule widths of larvae collected in summer, but the effect was not consistent across instars or source. Conversely, no significant endophyte effect on head capsule width was found in spring populations from either tillers or turves. This study shows that in irrigated dairy pasture, a high proportion of L. bonariensis larvae can live externally of tillers, presumably among the organic matter around the base of grasses in irrigated dairy pasture, and that density estimates based only on tiller populations will have significantly underestimated actual numbers. Having a precise indication of larval population densities is essential when developing life tables or determining economic damage threshold levels.     

Neighbour influence on the tiller demography of two perennial pampa grasses

Abstract. The aim of this study was to evaluate the possibility to use neighbour species composition to explain demographic variations in seasonal tillers in perennial grasses. Two warm-season species of the Argentina flooded pampa, Paspalum dilatatum and Sporobolus indicus, were used as models. Tiller structure and dynamics of target plants and the identity of their nearest neighbours were analyzed within a natural grassland community for an entire annual growth cycle. Canonical Correlation Analysis of tillering behaviour of target plants and neighbour species composition showed significant relationships for summer neighbourhood data. Community components affecting tiller demography were identified, and their spatial variation was described as different gradients of neighbourhood composition (NCG). NCG varied between target species, determining different spatial variation in neighbouring canopy dynamics and tiller dynamics. The tiller structure and dynamics of P. dilatatum plants were significantly correlated with the seasonal pattern of their neighbouring canopy density (NCD). Plants placed on the NCD-fluctuating extremes along NCG showed an unstable modular structure and short-lived tillers, as compared to those placed in the centre of the gradient. Relative density of the neighbouring canopy showed little variation along the NCG of S. indicus plants, which presented a tiller structure more stable and uniform than P. dilatatum plants did. Identification of NCG may be a promising approach to understanding changes in tiller dynamics of target species in relation to spatial and temporal changes in community structure.